1. Field
The present invention relates to a semiconductor optical device and a manufacturing method thereof, and more particularly, to a high-quality non-polar/semi-polar semiconductor device and a manufacturing method thereof. In the high-quality non-polar/semi-polar semiconductor device, a non-polar/semi-polar nitride semiconductor crystal is formed on a sapphire crystal plane, which enables the growth of a non-polar/semi-polar nitride semiconductor layer, in order that a piezoelectric effect generated in a polar nitride semiconductor layer may not occur in a nitride semiconductor layer. In addition, an InxAlyGa1-x-yN layer (0≦x≦1, 0≦y≦1, 0≦x+y≦1) is re-grown on a porous GaN layer formed on a template layer over a sapphire substrate to reduce the defect density of the GaN layer and improve the internal quantum efficiency and light extraction efficiency thereof.
2. Discussion of the Background
Since group III-V nitride semiconductors (also simply called “nitride semiconductors”), such as GaN, have excellent physical and chemical properties, they have recently been recognized as the essential material for semiconductor optical devices, such as a light emitting diode (LED), a laser diode (LD), and a solar cell. In general, group III-V nitride semiconductors are composed of a semiconductor material having an empirical formula of InxAlyGa1-x-yN (0≦x≦1, 0≦y≦1, 0≦x+y≦1). Such nitride semiconductor optical devices are applied as light sources for a variety of products, such as a keypad of a mobile phone, an electronic display board, and a lighting device.
In particular, as digital products using LEDs or LDs have evolved, there is an increasing demand for nitride semiconductor optical devices having higher brightness and higher reliability. For example, a side view LED used as a backlight of is a mobile phone is required to be brighter and thinner as the mobile phone tends to be slimmer. However, if a nitride semiconductor, such as polar GaN, is grown on a sapphire substrate using a C-plane (e.g., (0001) plane) as a sapphire crystal plane, the internal quantum efficiency may be reduced by a piezoelectric effect caused by the formation of a polarization field.
Accordingly, it is necessary to form a non-polar/semi-polar nitride semiconductor on a sapphire substrate. However, crystal defects, such as a line defect and an area defect, may be caused by a lattice mismatch between sapphire, which is suitable for the formation of a template layer using non-polar/semi-polar GaN or the like, and a non-polar/semi-polar nitride semiconductor template layer, which is formed on the sapphire, and a difference in coefficient of thermal expansion between constituent elements. Such crystal defects have a bad influence on the reliability of an optical device, for example, a resistance to electrostatic discharge (ESD), and are also the cause of current leakage within the optical device. As a result, the quantum efficiency of the optical device may be reduced, leading to the performance degradation of the optical device.
A variety of efforts have been made to reduce a crystal defect of a nitride semiconductor layer. One of these efforts is the use of a selective epitaxial growth. However, these efforts require high costs and complicated processes, such as SiO2 mask deposition. In addition, a crystal defect may be reduced by forming a low-temperature buffer layer on a sapphire substrate and then forming GaN thereon. However, this is not enough to solve a crystal defect problem of an optical device. Therefore, it is necessary to solve a problem that degrades the brightness and reliability of an optical device due to a crystal defect.